As science and technology advance rapidly, small and reliable sensors are used extensively in our living environments for transmitting various parameters of our environment such as an automatic detection of room temperature capable of fine tuning an air conditioning system can produce just enough cold air, or an automatic detection of abnormal heartbeat can avoid unrecoverable injuries caused by arrhythmias of a cardiac patient. Therefore, a timely, accurate and reliable data transmission and a high-efficiency energy source become increasingly important.
A magnetic diffusion (MD) data dissemination mechanism is developed from magnetic physical characteristics. Magnetic diffusion is a simple data dissemination mechanism for ensuring the timeliness and reliability of the data dissemination and provides a high efficiency of using an energy source, and whose principle is mainly based on the force interaction of magnets in the nature, wherein a data sink acts as a magnet, and data are like nails attracted by the data sink, and it is similar to the situation of having nails attracted by the magnets in the direction of a magnetic field. The magnetic field is created by setting an appropriate quantity of magnetic charges for each sensing node within a magnetic range of the data sink. The quantity of magnetic charges depends on a hop distance of the data sink and the resources provided by the data sink. After the magnetic field is created, data will be transmitted from a node with more magnetic charges to a node with less magnetic charges.
With reference to FIGS. 1 and 2 for schematic views of a data dissemination method of a conventional magnetic diffusion mechanism respectively, the magnetic diffusion dissemination mechanism needs to create a magnetic field before a data dissemination takes place, and nodes having different quantities of magnetic charges and a data sink are included within the magnetic field. In FIG. 1, a data sink 101 in a magnetic field 100 sets a maximum quantity of magnetic charges (such as 8). An interest message including the quantity of magnetic charges and the data sink 101 and a mode of the interest message are broadcasted periodically to a neighbor (which is a node), when a node receives an interest message for first time, and an item of the interest message will be produced and stored. The node will decrement the quantity of magnetic charges of the received interest message by 1, and the data type and the magnetic charges are recorded into the item, and the interest message is transmitted to the neighbor.
For every time of hopping a hop distance to a next node, the quantity of magnetic charges will be decremented by 1, and the same hop distance from the data sink 101 includes the same quantity of magnetic charges. If a node has received an interest message to produce an item and also received an interest message from another node, the node will compare the quantity of magnetic charges minus 1 included in the interest message with the quantity of magnetic charges in the item. If the quantity of magnetic charges included in the interest message after the decrement is still greater than the quantity of magnetic charges in the item, then the node will update the quantity of magnetic charges in the item as the numeric value minus 1 in the interest message, and transmit the interest message to its neighbor. If the quantity of magnetic charges included in the interest message after the decrement is smaller than the quantity of magnetic charges in the item, then the node will know that the interest message is not transmitted from a node close to the data sink 101 and will discard the interest message.
The magnetic field is created after the quantity of magnetic charges for each node is set according to the aforementioned sequence. The quantity of magnetic charges decreased from the data sink 101 to a plurality of sources A˜D guides the data to flow in an opposite direction, similar to the situation of a nail being attracted from a position with less magnetic charges towards a position with more magnetic charges in a magnetic field, and data are transmitted from a node with less magnetic charges to a node with more magnetic charges in the magnetic field.
In FIG. 1, nodes A and B have a hop distance from the data sink 101, and thus the quantity of magnetic charges is decremented by 1 to 7. Nodes C and D have the same quantity of magnetic charges which is equal to 6.
With reference to FIG. 2, the data sink 101 periodically broadcasts an interest message to each node, and the interest message specifically points out the data which is interested to the data sink 101 and possesses a data source node C in compliance with the interest message for selecting the shortest delay path from a multiple of paths according to the magnetic diffusion dissemination mechanism, and broadcasting the data to the data sink 101. With reference to FIG. 2, data 105 are disseminated from a data provider 103 to the data sink 101 along the path from the node C to a node with a large number of magnetic charges. The magnetic diffusion dissemination mechanism selects the shortest delay path, and thus a node A instead of a node B having the same quantity of magnetic charges hops a hop distance to reach the data sink 101.
However, the data dissemination of a wireless network is asymmetrical, meaning that valid data disseminations in a direction does not necessarily implies valid data disseminations in the opposite direction. With reference to FIG. 3 for a schematic view of a data dissemination with a data loss occurred in an asymmetrical wireless network for a conventional magnetic diffusion mechanism, if it is necessary to disseminate data 105 back through the node B, the node having a quantity of magnetic charges equal to 7 will transmit signals in all directions, such that the node having a quantity of magnetic charges equal to 8 (which is the data sink 101) will receive the signal. Due to the asymmetry of the wireless network, the node B is unable to return the data 105 to the data sink 101, and thus the node B is hindered from returning the data to the data sink 101 in a direction along the incremented magnetic charges, although the node B can complete setting the magnetic charges. Consequently, unreliable transmissions will result, and the way of looking for other nodes to disseminate data will cause a low using efficiency of energy sources.